Poster Presentation Melbourne Immunotherapy Spring Symposium 2025

Enhancing chimeric antigen receptor (CAR) T cell therapy for paediatric sarcoma through CAR T engineering and tumour microenvironment rewiring (#125)

Enola Roussel 1 2 , Esmee Broekhuizen 1 , Marit van Elsas 1 , Joe Zhu 1 2 , Vicky Qin 1 2 , Gianpietro Dotti 3 , Shahab Asgharzadeh 4 5 , Phillip Darcy 1 2 , Mawar Karsa 6 7 , Kevin sek 1 2 , Paul Neeson 1 2 , Klaartje Somers 6 7 , Deborah Meyran 1 2
  1. Cancer Immunology Program, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia
  2. The Sir Peter MacCallum Department of Oncology, Faculty of Medicine, Dentistry and Health Science, University of Melbourne, Melbourne, VIC, Australia
  3. Department of Microbiology and Immunology, University of North Carolina, Chapel Hill, NC, USA
  4. Children’s Hospital Los Angeles, Children’s Centre for Cancer and Blood Diseases, Division of Hematology, Oncology and Blood & Marrow Transplantation, and The Saban Research Institute, Los Angeles, CA, USA
  5. Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
  6. Children’s Cancer Institute, Lowy Cancer Research Centre, UNSW, Randwick, NSW, Australia
  7. School of Clinical Medicine, UNSW Medicine & Health, Sydney, NSW, Australia

Children and adolescents with metastatic/refractory sarcomas face a five-year survival rate of 30%. Furthermore, current therapies induce severe long-term treatment side effects in survivors, highlighting an urgent unmet clinical need for new treatments. Despite showing promising results in B-cell acute lymphoblastic leukaemia, chimeric antigen receptor (CAR) T cell therapy has shown limited efficacy in solid tumours, partially due to an immunosuppressive tumour micro-environment (TME). TME of paediatric sarcomas harbours immunosuppressive immune cell subsets and high TGF-β levels suppressing CAR T persistence/functionality.

We engineered second-generation CAR T cells targeting human B7-H3 with a TGF-β switch receptor to overcome TGF-β immunosuppression. The cells phenotype (TSTEM-like) was maintained to promote persistence and their function was assessed in vitro using sarcoma cell lines. We tested the small-molecule curaxin CBL0137 for its immunomodulatory and TME-rewiring potential in an immunocompetent fibrosarcoma mouse model (24JK) using Cytek® spectral flow cytometry, LegendplexTM, and AlphaLISA®. 

Both B7-H3 TSTEM-like CAR T and B7-H3 TSTEM-like TGF-β switch CAR T demonstrated effective cytotoxicity and cytokine secretion against B7H3+ osteosarcoma cell lines. The 24JK model exhibited high baseline TGF-β levels and abundant M2-like macrophages. CBL0137 treatment led to increased infiltration of NK cells, cytotoxic CD8+ T cells (Grz+, CD39+/PD-1+), eosinophils, and reduced immunosuppressive M2-like macrophage populations. Moreover, CBL0137 treatment upregulated CXCL1 and CXCL10. 

Our preclinical data support the therapeutic potential of combining CAR T cell with TME modulation for paediatric sarcoma. CAR T cells demonstrated antigen-specific killing, while CBL0137 favoured TME anti-tumour immunity. This combinatorial approach could overcome key barriers to immunotherapy in solid tumours, reduce reliance on toxic conventional therapies, and significantly improve outcomes of patients.